The invention relates to the field of ink-jet printers used for colour printing of large format articles used, in particular, in the advertisement industry.
A specific feature of the utilization of ink-jet printers used for colour printing of large format articles is the production of large size images (up to tens of square meters) of sufficiently high quality at relatively low cost, which is attained by creating highly-productive machines with relatively low resolution of the produced images (usually 18-36 lines per inch). In a principle respect these devices are not distinctive over ordinary printers that are widely used as documenting devices in personal computers (PC).
A typical representative of such devices is an ink-jet printing head and a printer comprising a paper feeding device, a carriage executing reciprocal movement along a paper substrate, and a removable jet head with a reserve of ink that is mounted on the carriage (EP, A2 0400652, 1990, B 41 J 2/07). The head is made in the form of an autonomous unit having an electronic unit in which information relating to the mutual positioning of the drawing nozzles in the head is entered. These nozzles are used by the control program of the PC when information is fed from the PC to the printer.
The process of drawing is carried out by supplying energy to each nozzle of the head in the form of an electrical pulse which is converted into heat sufficient to discharge a portion of ink from the nozzle. Furthermore, a system for synchronizing the position of the head relative to the substrate and the information being presented is used in the printer.
From a principle point of view, all printers operate according to this arrangement, differing only by the method of applying the image (either by heat, or hydraulic impact, or blast of air, etc.)
All of the basic elements of such printers are present in the device disclosed in the patent U.S. Pat. No. 4,999,651, 1991, G 01 D 15/16. In a colour recorder, ink cartridges are positioned on a common carriage that effects reciprocal movement. There are also intermediate working cartridges in which the level of the ink is maintained virtually constant, which ensures the highest quality of the images being reproduced. Furthermore, the device contains an electronic unit which holds the image being reproduced in its memory and controls the operation modes of the device.
The presence of an intermediate unit for storing the information to be applied makes it possible to separate in time the generation of images in a PC (for example, by scanning photographic images and then editing them, or producing images by machine graphic methods, etc.) and their transfer to the substrate. Furthermore, the volume of the information stored in the device only depends on its own capabilities and is in no way related to the PC, which makes it possible to use this device in network systems.
The presence of ink cartridges directly on the carriage simplifies the construction of the device, ensuring at the same time the possibility of obtaining a larger volume of graphic material without frequently recharging the device. As already noted above, the presence of an intermediate service cartridge ensures a constant level of the ink, which promotes effective operation of the jet elements and a high quality of the images being reproduced.
A device is known that serves to obtain a direct image on one side of a sheet and a mirror image on the other side, which makes it possible to obtain a high quality image on a semi-transparent material (U.S. Pat. No. 5,376,957, 1994, B 41 J 2/045). This device is provided with an ink-feeding mechanism with two carriages positioned on opposite sides of a substrate. Control of the operation of the device and, in particular, the carriages and heads, is carried out with the aid of a unit for control and storage of the direct and mirror images being formed. By means of a scanner, information is entered into a computer which edits the image and encodes the print density of each colour in the form of electrical current pulses of different width, which control electric valves of the atomizers of the jet heads of each colour, which are on the ink-jet printing device. Thus, the density of each colour is determined by the width of the pulse generated by the PC. Specific features of the operation of ink-jet elements of the heads are that the air stream entering the working nozzle of the jet element consists of two streams: onexe2x80x94continuous, creating a constant stream of air in the nozzle, which ensures that the ink in the supply channel does not dry and hinders the formation of parasitic drops at the end of that channel, and the secondxe2x80x94controlled with the aid of an air valve which opens an additional stream of air, ensuring the supply of ink to the substrate in accordance with the width of the control pulses. In order to ensure reliable adhesion and drying and to exclude smearing of the ink, the substrate is heated with spiral heaters which are mounted below and above the carriages in the direction of movement of the substrate. Sponges are also disposed on the carriages, the sponges wiping the substrate before the ink is applied thereon, this ensuring removal of foreign contaminants and also enhancing application of the ink onto the substrate.
However, the presence of lines in each moving carriage should be noted in this construction. These lines consist of a plurality of electrical cables, for control of the valves in the heads, and tubes for feeding the ink. This line increases as the width of the substrate, along which the carriage moves, increases, and this line has to move together with the carriage, which creates a number of technological difficulties and reduces the reliability of operation of the device.
Reciprocal movement of the carriages presumes acceleration to the nominal speed, braking and stopping for each working cycle, which reduces the productivity of the device and requires increased power of the drive mechanisms and corresponding braking dampers. Furthermore, with horizontal positioning of the heads of different colours from the left to the right and from the right to the left, the sequence in which the primary colours are applied is disturbed, which results in xe2x80x9cstripingxe2x80x9d (by shade) of the obtained images. There is also a problem in obtaining quality two-sided images, the solution to this problem not being found in prior art. In particular, different heads, positioned on different carriages, are used in the making of direct and mirror images. It is virtually impossible to ensure their complete identicality in operation. Therefore, when two-sided images are being produced, distortions inevitably occur in the colour reproduction, and this affects the quality of the article.
The problems being solved in the invention are the following:
liquidation of the lines connecting the carriage to the systems for supplying control signals, air and ink;
ensure the successive application of the primary colours;
suppression of colour aberrations when printing a semi-transparent substrate on both sides;
ensure the precise application of the ink onto the substrate;
ensure the possibility of simultaneously performing one-sided printing on two substrates.
In order to achieve the aforesaid technical results, the construction of a large format ink-jet colour printer is proposed which comprises a substrate feeding system, an ink feeding mechanism which is movable along a closed guiding rail relative to the substrate, this making it possible for heads to travel around the substrate on two sides, and a printer control unit. Shafts in the substrate feeding system are positioned in a vertical plane, wherein tensioning shafts, connected to reversible motors by means of magnetic clutches, are positioned above and below the feeding shaft provided with a reversible motor. The ink feeding mechanism, movable along the closed guiding rail is provided with at least one carriage with brushes for supplying electric power, with a receiver to be filled with air from an external source by means of a rapidly-released catch, with a controller provided with a transceiver, and with an optical sensor electrically coupled to the controller. The guiding rail is provided with busbars for supplying electric power and with a hatched ruler for exactly positioning the carriage. Wherein, electrical valves connected to the printer control unit are mounted between the charging cartridges, positioned on the carriage and having a level sensor, and the rapidly-released catches of the system for recharging those cartridges. The rapidly-released catches are positioned in places where the guiding rail turns. In order to increase the productivity there may be two and more of such carriages. The carriages move at a constant speed, which reduces the power of the drive mechanisms and eliminates the need for dampers, since movement of the carriages takes place in one direction (for example, in the clockwise direction), removes the question of xe2x80x9cstripingxe2x80x9d in the obtained images, and the colour palette of the direct and mirror images is also the same. Wherein, full autonomy of the carriage is ensured upon its movement over the working sections of the substrates.
The printer may have a second substrate feeding system, independent of the first, wherein both parallel positioned substrate systems are encompassed by the closed guiding rail. Thus, an image may be obtained simultaneously on two substrates which are inside the closed guiding rail, this substantially expanding the consumer properties of the device and enhancing its productivity.